This invention concerns fuel injectors for internal combustion engines. Fuel injection has become the preferred mode of delivering fuel charges to the cylinders of engines used in automobiles and trucks.
Fuel injectors typically include a thin elongated valve element commonly referred to as a valve "needle", which has a partially spherical tip, the tip engaging a conical seat when the injector is closed to prevent fuel from being injected into the engine from the injector until the injector is opened. Energizing an injector solenoid operator causes the needle to be lifted from the seat when fuel is to be injected, allowing fuel under pressure to be discharged through an aligned opening in the seat, and through an orifice in a plate below the valve seat. The orifice influences the shape of a spray pattern formed when the pressurized fuel discharges from the injector tip.
The shape and surface finish of the needle tip is critical for proper operation of the injector, primarily because the tip must very reliably establish a sealing engagement with the valve seat whenever the solenoid is deenergized.
The tip end initially is ground to a partially spherical shape. A "superfinishing" procedure is then conducted to reliably achieve proper sealing of each fuel injector tip on its seat. The superfinishing is carried out using a very fine grit stone and a compliant mounting of the needle to achieve a submicron surface finish.
Current multivalve engines employ injectors which divide the discharge into two distinct spray patterns, each directed at a respective intake valve associated with a given engine cylinder. This dual spray pattern is achieved by an orifice disc having two orifice openings and by a modification of the partially spherical needle tip, comprised of a conical spray-shaping feature extending from the center of the tip. Other spray pattern affecting features are also possible.
The spray-shaping feature has been difficult to form while carrying out shaping and superfinishing of the annular region of the spherical needle tip which engages the conical valve seat.
It is the object of the present invention to provides a fuel injector needle tip which enables a central spray pattern shaping feature to be provided on the tip while allowing a properly finished annular valve seat engaging region on the needle tip.